Satellite communications systems and methods are widely used for radioterminal communications. Satellite radioterminal communications systems and methods generally employ at least one space-based component, such as one or more satellites, that is/are configured to wirelessly communicate with a plurality of satellite radioterminals.
A satellite radioterminal communications system or method may utilize a single antenna pattern (beam) covering an entire area served by the system. Alternatively, or in combination with the above, in cellular satellite radioterminal communications systems and methods, multiple antenna patterns (beams or cells) are provided, each of which can serve a substantially distinct geographical area in an overall service region, to collectively serve an overall satellite footprint. Thus, a cellular architecture similar to that used in conventional terrestrial cellular/PCS radioterminal systems and methods can be implemented in cellular satellite-based systems and methods. The satellite typically communicates with radioterminals over a bidirectional communications pathway, with radioterminal communications signals being communicated from the satellite to the radioterminal over a downlink or forward link, and from the radioterminal to the satellite over an uplink or return link. The downlink and uplink may be collectively referred to as service links.
The overall design and operation of cellular satellite radioterminal systems and methods are well known to those having skill in the art, and need not be described further herein. Moreover, as used herein, the term “radioterminal” includes cellular and/or satellite radioterminals with or without a multi-line display; Personal Communications System (PCS) terminals that may combine a radioterminal with data processing, facsimile and/or data communications capabilities; Personal Digital Assistants (PDA) that can include a radio frequency transceiver and/or a pager, Internet/Intranet access, Web browser, organizer, calendar and/or a global positioning system (GPS) receiver; and/or conventional laptop and/or palmtop computers or other appliances, which include a radio frequency transceiver. As used herein, the term “radioterminal” also includes any other radiating user device/equipment/source that may have time-varying or fixed geographic coordinates, and may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based), or situated and/or configured to operate locally and/or in a distributed fashion at any other location(s) on earth, above the earth and/or in space. A “radioterminal” also may be referred to herein as a “radiotelephone,” “terminal”, “wireless terminal” or “wireless user device”. Furthermore, as used herein, the term “base station” or “ancillary terrestrial component” includes any radiating device that is configured to provide communications service to one or more radioterminals and may have time-varying or fixed geographic coordinates, may be portable, transportable, installed in a vehicle (aeronautical, maritime, or land-based), or situated and/or configured to operate locally and/or in a distributed fashion at any other location(s) on earth, above the earth and/or in space.
Cellular satellite communications systems and methods may deploy hundreds of cells (i.e., antenna patterns), each of which corresponds to one or more spot beams, over a satellite footprint corresponding to a service area. It will be understood that large numbers of cells may be generally desirable, since the frequency reuse and the capacity of a cellular satellite communications system or method may both increase in direct proportion to the number of cells. Moreover, for a given satellite footprint or service area, increasing the number of cells may also provide a higher gain per cell, which can increase the link robustness and improve the quality of service.
The uplink and downlink communications between the wireless terminals and a satellite may utilize one or more air interfaces, including proprietary air interfaces and/or conventional terrestrial cellular interfaces, such as Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA) and/or Code Division Multiple Access (CDMA) air interfaces. A single air interface may be used throughout the cellular satellite system. Alternatively, multiple air interfaces may be used for the satellite communications. See, for example, U.S. Pat. No. 6,052,560, issued Apr. 18, 2000, entitled Satellite System Utilizing a Plurality of Air Interface Standards and Method Employing the Same, by the present inventor Karabinis. In general, regardless of the air interface or interfaces that are used, each satellite cell generally uses at least one carrier/channel to provide service. Thus, a return service link and/or a forward service link may use one or more carriers/channels to provide service.
The above description has focused on communications between the satellite and the wireless terminals. However, cellular satellite communications systems and methods also generally employ a bidirectional feeder link for communications between a terrestrial satellite gateway and the satellite. The bidirectional feeder link includes a forward feeder link from the gateway to the satellite and a return feeder link from the satellite to the gateway. The forward feeder link and/or the return feeder link each may use one or more carriers/channels.
Terrestrial networks can enhance cellular satellite radioterminal system availability, efficiency and/or economic viability by terrestrially using/reusing at least some of the frequencies that are allocated to cellular satellite radioterminal systems. In particular, it is known that it may be difficult for cellular satellite radioterminal systems to reliably serve densely populated areas, because satellite signals may be blocked by high-rise structures and/or may not penetrate into buildings. As a result, satellite frequencies may be underutilized or unutilized in such areas. The terrestrial use/reuse of at least some of the satellite system frequencies can reduce or eliminate this potential problem.
Moreover, the capacity of a hybrid system, comprising terrestrial and satellite-based connectivity and configured to terrestrially use/reuse at least some of the satellite-band frequencies, may be higher than a corresponding satellite-only system since terrestrial frequency use/reuse may be much denser than that of the satellite-only system. In fact, capacity may be enhanced where it may be mostly needed, i.e., in densely populated urban/industrial/commercial areas where the connectivity/signal(s) of a satellite-only system may be unreliable. As a result, a hybrid (satellite/terrestrial cellular) system that is configured to use/reuse terrestrially at least some of the frequencies of the satellite band may become more economically viable, as it may be able to serve more effectively and reliably a larger subscriber base.
Satellite radioterminal communications systems and methods that may employ terrestrial use of satellite frequencies are described in U.S. Pat. Nos. 6,684,057 to Karabinis, entitled Systems and Methods for Terrestrial Reuse of Cellular Satellite Frequency Spectrum; 6,785,543 to Karabinis, entitled Filters for Combined Radiotelephone/GPS Terminals; 6,856,787 to Karabinis, entitled Wireless Communications Systems and Methods Using Satellite-Linked Remote Terminal Interface Subsystems; 6,859,652 to Karabinis et al., entitled Integrated or Autonomous System and Method of Satellite-Terrestrial Frequency Reuse Using Signal Attenuation and/or Blockage, Dynamic Assignment of Frequencies and/or Hysteresis; and 6,879,829 to Dutta et al., entitled Systems and Methods for Handover Between Space Based and Terrestrial Radioterminal Communications, and For Monitoring Terrestrially Reused Satellite Frequencies At a Radioterminal to Reduce Potential Interference; and Published U.S. Patent Application Nos. US 2003/0054761 to Karabinis, entitled Spatial Guardbands for Terrestrial Reuse of Satellite Frequencies; US 2003/0054814 to Karabinis et al., entitled Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0073436 to Karabinis et al., entitled Additional Systems and Methods for Monitoring Terrestrially Reused Satellite Frequencies to Reduce Potential Interference; US 2003/0054762 to Karabinis, entitled Multi-Band/Multi-Mode Satellite Radiotelephone Communications Systems and Methods; US 2003/0224785 to Karabinis, entitled Systems and Methods for Reducing Satellite Feeder Link Bandwidth/Carriers In Cellular Satellite Systems; US 2002/0041575 to Karabinis et al., entitled Coordinated Satellite-Terrestrial Frequency Reuse; US 2003/0068978 to Karabinis et al., entitled Space-Based Network Architectures for Satellite Radiotelephone Systems; US 2003/0153308 to Karabinis, entitled Staggered Sectorization for Terrestrial Reuse of Satellite Frequencies; and US 2003/0054815 to Karabinis, entitled Methods and Systems for Modifying Satellite Antenna Cell Patterns In Response to Terrestrial Reuse of Satellite Frequencies, all of which are assigned to the assignee of the present invention, the disclosures of all of which are hereby incorporated herein by reference in their entirety as if set forth fully herein.
Some satellite radiotelephone systems and methods may employ interference cancellation techniques to allow terrestrial reuse of satellite frequencies. For example, as described in U.S. Pat. No. 6,684,057, cited above, a satellite frequency can be reused terrestrially by an ancillary terrestrial network even within the same satellite cell, using interference cancellation techniques. In particular, a system according to some embodiments of U.S. Pat. No. 6,684,057 includes a space-based component that is configured to receive wireless communications from a first radiotelephone in a satellite footprint over a satellite radiotelephone frequency band, and an ancillary terrestrial network that is configured to receive wireless communications from a second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band. The space-based component also receives the wireless communications from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band as interference, along with the wireless communications that are received from the first radiotelephone in the satellite footprint over the satellite radiotelephone frequency band. An interference reducer is responsive to the space-based component and to the ancillary terrestrial network that is configured to reduce the interference from the wireless communications that are received by the space-based component from the first radiotelephone in the satellite footprint over the satellite radiotelephone frequency band, using the wireless communications that are received by the ancillary terrestrial network from the second radiotelephone in the satellite footprint over the satellite radiotelephone frequency band.
Other radiotelephone systems and methods can monitor terrestrial reuse of satellite-band frequencies to reduce potential interference. For example, as described in Published U.S. Patent Application No. US 2003/0054814 A1, cited above, radiation by an ancillary terrestrial network, and/or satellite radiotelephones that communicate therewith are monitored and controlled, to reduce and preferably prevent intra-system interference and/or interference with other satellite radiotelephone systems. In particular, a satellite radiotelephone system includes a space-based component that is configured to wirelessly communicate with first radiotelephones in a satellite footprint over a satellite radiotelephone frequency band, and an ancillary terrestrial network that is configured to wirelessly communicate with second radiotelephones in the satellite footprint over at least some of the satellite radiotelephone frequency band, to thereby terrestrially reuse the at least some of the satellite radiotelephone frequency band. Wireless radiation by the ancillary terrestrial network and/or the second radiotelephones at the space-based component is monitored, and the radiation by the ancillary terrestrial network and/or the plurality of second radiotelephones is adjusted in response to the monitoring. Intra-system interference and/or interference with other satellite systems thereby may be reduced or prevented. See the Abstract of U.S. Published Patent Application US 2003/0054814 A1.
Finally, additional systems and methods may be used to monitor terrestrially reused satellite frequencies to reduce potential interference. For example, as described in Published U.S. Patent Application No. US 2003/0073436 A1, cited above, a satellite radiotelephone system includes a space-based component, an ancillary terrestrial network, a monitor and a controller. The space-based component is configured to wirelessly communicate with radiotelephones in a satellite footprint over a satellite radiotelephone frequency band. The satellite footprint is divided into satellite cells in which subsets of the satellite radiotelephone frequency band are spatially reused in a spatial reuse pattern. The ancillary terrestrial network is configured to wirelessly communicate with radiotelephones in the satellite footprint over at least some of the satellite radiotelephone frequency band, to thereby terrestrially reuse the at least some of the satellite radiotelephone frequency band. The monitor is configured to monitor wireless radiation at the space-based component that is produced by the ancillary terrestrial network and/or the radiotelephones in satellite cells that adjoin a satellite cell and/or in the satellite cell, in at least part of the subset of the satellite radiotelephone frequency band that is assigned to the satellite cell for space-based component communications. The controller is configured to adjust the radiation by the ancillary terrestrial network and/or the radiotelephones, in response to the monitor. See the Abstract of U.S. Published Patent Application U.S. 2003/0073436 A1.
A Mobile Satellite System (MSS) 100 is shown in FIG. 1. The MSS 100 includes at least one gateway 102 that includes an antenna 104 and gateway electronics 106 that can be connected to other networks 108 including terrestrial and/or other radiotelephone networks. The gateway 102 also communicates with at least one Space-Based Component (SBC) 110, such as a satellite, over a satellite feeder link 109.
The SBC 110 is configured to transmit wireless communications to a plurality of ancillary terrestrial radioterminals 120a, 120b in a satellite footprint that includes one or more satellite cells 130 over one or more satellite forward link (downlink) frequencies fD. The SBC 110 is configured to receive wireless communications from, for example, a first radioterminal 120a in the satellite cell 130 over a satellite return link (uplink) frequency fU.
The MSS 100 also includes an Ancillary Terrestrial Network (ATN) that includes at least one Ancillary Terrestrial Component (ATC) 140. The ATC 140 can include a base station transceiver that is configured to service radioterminals within its service area cell by terrestrially reusing satellite frequencies that are used by the SBC 110. For example, as shown in FIG. 1, the ATC 140 is configured to transmit wireless communications to a second radioterminal 120b within ATC cell 150 over a satellite downlink frequency f′D which may be the same as the satellite downlink frequency fD, and to receive from the second radioterminal 120b over a satellite uplink frequency f′U which may be the same as the satellite uplink frequency fU Accordingly, the radioterminal 120a may be communicating with the SBC 110 while the radioterminal 120b may be communicating with the ATC 140 over a frequency range that at least partially overlaps. The gateway 102 may communicate with the ATC 140 over a terrestrial link 160.
Because the satellite uplink and downlink frequencies fU, fD, f′U, f′D may at least partially overlap, communications between the SBC 110 and the first radioterminal 120a can interfere with communications between the second radioterminal and the ATC 140 and vice versa. Moreover, communications between the second radioterminal and the ATC 140 can also interfere with communication by components of another MSS. For example, as shown in FIG. 1, another MSS includes a SBC 170 that communicates with a radioterminal 172 over satellite communication frequencies that at least partially overlap with and/or are adjacent to the satellite uplink and downlink frequencies fU, fD, f′U, f′D used by the MSS 100. The radioterminal 172 is configured to communicate with the SBC 170 and it may be further configured to terrestrially communicate with an ATN using satellite frequencies such as explained above for the radioterminals 120a-b. The radiated signals from the radioterminals 120a-b and ATC 140 may interfere with communications between the SBC 170 and the radioterminal 172. When MSSs have adjacent or overlapping cells and are owned or controlled by different entities, it may be more difficult to employ some of the interference cancellation techniques described above and such interference to an MSS may be considered more objectionable when it is caused by another MSS owned/controlled by another entity.
The Federal Communications Commission has proposed to reduce/avoid such interference to MSSs through the regulation of the terrestrial use/reuse of satellite frequencies based on an analytical model it developed to define limits on uplink interference potential to an L-band MSS from the deployment of an ATN. See, Report and Order and Notice of Proposed Rulemaking, FCC 03-15, Flexibility for Delivery of Communications by Mobile Satellite Service Providers in the 2 GHz Band, the L-Band, and the 1.6/2.4 Bands, IB Docket No. 01-185, Adopted: Jan. 29, 2003, Released: Feb. 10, 2003, hereinafter referred to as “Order FCC 03-15”. Also, see Memorandum Opinion and Order and Second Order on Reconsideration, FCC 05-30, In the matter of Flexibility for Delivery of Communications by Mobile Satellite Service Providers in the 2 GHz Band, the L-Band, and the 1.6/2.4 GHz Bands, IB Docket No. 01-185, Adopted: Feb. 10, 2005, Released: Feb. 25, 2005.